THE  SEPARATION  OF  LANTHANUM 
AND  PRASEODYMIUM 


By 

JOHN  WIERDA 

A.B.  Hope  College,  1921 


THESIS 

SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 
FOR  THE  DEGREE  OF  MASTER  OF  SCIENCE  IN  CHEMISTRY 
IN  THE  GRADUATE  SCHOOL  OF  THE  UNIVERSITY 
OF  ILLINOIS,  1922 


URBANA,  ILLINOIS 


. 


, . 


1322 
W 6 3 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 


July  29  1922 


1 HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY John  WIer&a 

ENTITLED  The  Separation  of  Lanthanum  and  Prase odymium. 


BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 


THE  DEGREE  OF 


ScLene© 


In  Charge  of  Thesis 


Acting  Head  of  Department 


Recommendation  concurred  in* 


•o  1 vn 


Committee 


on 


Final  Examination* 


Required  for  doctor’s  degree  but  not  for  master’s 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/separationoflantOOwier 


CONTENTS 


Page 

ACKNOWLEDGMENT 

I.  INTRODUCTION  1 

II.  HISTORICAL  1 

III.  METHODS  USED  3 

IV.  EXPERIMENTAL  3 

Magnesium  Oxide  Separation  3 

Precipitation  by  NH4OH  in  Presence  of  Ammonium  7 

Salts 

Partial  Decomposition  of  the  Nitrate  8 

V.  COMPARISON  OF  METHODS  8 

VI.  SUMMARY  10 

VII.  BIBLIOGRAPHY  11 


ACKNOWLEDGMENT 


The  writer  wishes  to  express  his  appreciation 
to  Dr.  H.  C.  Kremers  under  whose  direction  this  in- 
vestigation was  carried  out. 


1 


THE  SEPARATION  OF  LANTHANUM  AND  PRAESODYMIUM 

I.  INTRODUCTION. 

Lanthanum  and  praseodymium  are  two  of  the  so-called  rare  earth 
elements  occupying  adjacent  positions  in  the  periodic  table  and  re- 
sembling each  other  very  closely  in  chemical  properties.  On  account 
of  this  resemblance  it  is  not  only  impossible  to  effect  a quantita- 
tive separation  of  the  two  but  it  is  very  difficult  to  obtain,  even, 
the  major  portion  of  either,  free  from  the  other.  The  object  of 
this  investigation  was  to  compare  several  of  the  reported  methods  in 
order  to  determine  which  one  should  prove  the  most  satisfactory  for 
the  separation  of  these  elements,  one  of  which  is  to  be  used  in  a 
subsequent  investigation. 

II.  HISTORICAL. 

Methods  used  for  the  separation  of  the  rare  earths  are  divided 
into  the  following  four  classes: 

I.  Separation  by  fractional  crystallization  of  salts. 

II.  Separation  by  fractional  precipitation. 

III.  Separation  by  means  of  processes  of  oxidation. 

IV.  Separation  by  physical  methods. 

The  salts  that  can  be  used  best  for  the  separation  of  lanthanum 
and  praseodymium  by  fractional  crystallization  are  the  sulphates, 
the  double  ammonium  nitrates,  the  double  magnesium  nitrates,  and  the 
ethyl  sulphates.  Mosander1  separated  didymium  (praseo-  and  neody- 
mium) from  lanthanum  by  use  of  the  former.  Mendeleeff2,  and  later 


2 


von  Wellsbach3,  used  the  double  ammonium  nitrates  for  the  same  pur- 
pose, the  former  using  an  aqueous  and  the  latter  a nitric  acid  solu- 
tion. Drossbach"  introduced  the  use  of  double  magnesium  nitrates. 
Spencer5  states  that  ethyl  sulphates  can  be  used  for  f ractionating 
a lanthanum-didymium  mixture,  when  neodymium  concentrates  in  the 
first  fraction  and  lanthanum  in  the  last. 

Of  the  above  methods  the  one  most  commonly  used  is  the  second. 
The  process  is  slow  and  tedious.  Spencer0  in  "The  Metals  of  the 
Rare  Earths"  says:  "Despite  the  large  amount  of  material  used  by  von 
Wellsbach,  and  the  large  number  of  recrystallizations  carried  out, 
it  is  extremely  doubtful  whether  he  ever  got  praseodymium  free  from 

it 

lanthanum.  The  double  magnesium  nitrates  answer  well  for  the  sepa- 
ration of  praseo-  and  neodymium  but  are  not  nearly  as  efficient  for 
effecting  a separation  of  praseodymium  and  lanthanum. 

The  separation  by  fractional  precipitation  includes  the  partial 
decomposition  of  the  nitrates  and  precipitation  methods  employing 
magnesium  oxide,  oxalic  acid  or  oxalates,  ammonia,  caustic  alkalies, 
organic  bases,  sodium  sulphite,  and.  ammonium  or  alkali  carbonates. 

A method  recently  devised  by  Prandtl  and.  Rauchenberger7  consists  in 
precipitating  the  didymium  with  ammonia  in  the  presence  of  ammonium 
salts  which  cause  the  lanthanum  to  remain  in  solution. 

Oxidational  processes  can  only  be  used  for  separating  cerium  and 
thorium  from  the  rare  earths.  They  cannot  be  used  to  separate  the 
rare  earths  themselves,  due  to  the  fact  that  the  latter  consistently 
display  a valence  of  three  in  all  their  salts. 


' 


- 


<* 


. 


. 


. 


. 


. 

- 


3 


The  physical  methods  of  separation  consist  of  absorption,  dis- 

e CL 

tillation,  and  electrolysis.  Hofman  and  Kriiss  found  that  solution 
of  rare  earths  with  an  equivalent  weight  of  R111  = 116.8  after  shak- 
ing with  charcoal  and  filtering,  possessed  an  equivalent  weight  of 
Riii  = 134.4.  The  amount  of  charcoal  necessary,  however,  is  large 
since  the  amount  of  material  absorbed  is  small  in  comparison  to  the 
amount  used.  Investigation  of  distillation  methods  has  failed  to 
reveal  anything  promising  except  for  the  separation  of  scandium  and 
thorium.  Dennis  and  Lemon9  by  ten  repetitions,  - that  is  redissolv- 
ing the  precipitated  hydroxides  and  resubmitting  them  to  electrolysis  , 
succeeded  in  separating  pure  lanthanum  from  didymium. 

III.  METHODS  USED. 

The  methods  tried  out  during  this  investigation  we re  (1)  the 
partial  decomposition  of  the  nitrates,  (2)  fractional  precipitation 
by  means  of  magnesium  oxide  and  (3)  fractional  precipitation  by 
means  of  ammonium  hydroxide  in  the  presence  of  ammonium  salts. 

IV.  EXPERIMENTAL • 

Magnesium  Oxide  Separation. 

For  a preliminary  trial  a quantity  of  praseodymium  oxide  contain- 
ing some  neodymium  and  lanthanum  was  dissolved  in  nitric  acid  and  the 
solution  filtered.  The  boiling  solution  was  then  treated  with  mag- 
nesium oxide  in  the  powdered  form.  The  d.ry  oxide  forms  pasty  glo- 
bules when  added  to  the  solution  and  these  adhere  together  firmly 
being  broken  up  only  by  long  continued  boiling.  Thereafter  a thin 
paste  was  made  by  add_ing  water  slowly  to  the  oxide  and  stirring. 


- 


. 


4 


Afterwards,  however,  it  was  noted  that  if  the  water  were  added  rapid- 
ly and  the  material  stirred  vigorously  at  the  same  time  the  oxide 
remained  in  suspension  without  forming  any  pasty  material,  whatso- 
ever. This  could  then  he  stirred  and  poured  into  the  rare  earth 
solution  at  any  rate  desired.  Enough  magnesium  oxide  was  added  to 
precipitate  part  of  the  rare  earths,  v/hich  were  then  filtered  off 
and  washed.  The  precipitate  was  rather  granular  and  filtered  easily. 

Before  and  after  the  first  precipitation  the  solution  was  tested 
spectroscopically.  Praseodymium  absorption  lines  showed  very  plainly 
each  time.  Neodymium  lines  were  distinct  but  not  very  heavy  before 
precipitation.  In  the  filtrate  after  the  first  precipitation  they 
were  very  faintly  visible.  (It  may  be  advisable  to  say  here  that 
all  spectroscopic  examinations  were  made  by  examining  the  solution 
in  a quartz  box  of  4 cm.  by  1 cm.  internal  dimensions). 

The  solution  was  then  treated  with  about  the  same  amount  of  mag- 
nesium oxide.  More  precipitate  was  obtained  than  in  the  former  pre- 
cipitation, due,  evidently,  to  the  fact  that  the  original  solution 
was  slightly  acid  and  part  of  the  oxide  was  used  in  neutralizing 
this  acidity.  After  precipitation  there  were  no  absorption  lines 
visible  in  the  spectrum,  showing  the  absence  of  both  praseodymium 
and  neodymium.  The  solution  was  then  acidified  with  dilute  nitric 
acid  and  tested  for  lanthanum  by  adding  oxalic  acid  solution.  No 
precipitate  was  obtained,  indicating  that  the  rare  earths  had  all 
been  precipitated. 

The  first  precipitate  obtained  was  dried  and  weighed.  (All 
weighings  were  made  on  platform  balances  and  are  only  approximately 


5 


correct).  It  amounted  to  48  grams.  Some  lanthanum  oxalate  was  then 

reduced  to  the  oxide  by  ignition  in  an  electric  furnace.  The  pra- 

$’  c,/"' 

seodymium  precipitate  and/  the  lanthanum  residue  was  then  dissolved 
in  nitric  acid  and  the  solution  filtered.  Spectroscopic  analysis 
indicated  neodymium  lines  when  viewed  thru  4 cm.  of  solution,  none 
thru  1 cm.  The  excess  acidity  was  neutralized  by  adding  carefully 
magnesium  oxide  to  neutral  reaction  to  litmus.  6 grams  magnesium 
oxide  were  then  added.  After  filtering  and  drying  25  grams  of  pre- 
cipitate were  obtained.  The  color  of  it  was  light  green.  Neodymium 
lines  were  still  present  in  the  filtrate  but  very  light.  The  precip- 
itation was  repeated  with  the  same  amount  of  magnesium  oxide.  24 
grams  of  precipitate  were  obtained.  The  color  was  the  same  as  the 
previous  precipitate.  Neodymium  lines  were  absent  from  the  fil- 
trate. Two  precipitations  were  then  made  using  4 grams  of  the  oxide 
for  each.  The  color  of  the  first  precipitate  amounting  to  21  grams, 
was  still  greenish  but  lighter  than  the  first  two.  The  second  pre- 
cipitate, amounting  to  19  grams,  was  white.  Praseodymium  lines  were 
evident  in  the  filtrate  after  the  first  precipitation  with  4 grams 
of  the  oxide  but  not  after  the  second.  Upon  concentrating  the  solu- 
tion, however,  they  reappeared.  Thereupon  1 gram  magnesium  oxide 
v/ as  added.  5 grams  of  precipitate,  were  obtained.  No  prase odynium 
lines  were  visible  until  the  solution  was  concentrated  still  further, 
and  then  only  the  line  at  483.  The  line  at  444  was  entirely  absent. 
The  solution  v/as  then  acidified  with  nitric  acid  and  the  lanthanum 
precipitated  with  oxalic  acid.  50  grams  of  dried  lanthanum  oxalate 
were  obtained  showing  that  there  v/as  still  considerable  lanthanum 
in  solution. 


f 


6 

To  try  out  the  method  on  a somewhat  larger  scale  and  to  deter- 
mine whether  all  the  praseodymium  could  he  removed,  by  precipitation 
with  magnesium  oxide  the  upper  fractions  of  a double  magnesium  ni- 
trate series  were  used#  Both  contained  lanthanum  and  praseodymium 
but  no  neodymium.  The  saturated  liquid  of  the  two  fractions  was 
filtered  and  the  crystallized,  part  dissolved  in  water  and  filtered. 
The  total  filtrate  was  then  heated  on  a steam  bath  and  treated  in- 
termittently with  small  amounts  of  magnesium  oxide  suspended  in 
water.  After  a considerable  precipitate  had  formed  it  was  filtered, 
dried  and  weighed  and  the  process  repeated.  After  a couple  precipi- 
tations the  praseodymium  lines  became  weaker  and  the  amount  of  the 
precipitate  was  decreased.  After  five  precipitations  of  138,  108, 
20,  23,  and  31  grams  respectively,  the  praseodymium  lines  were  only 
faintly  visible.  To  obtain  an  idea  of  hov/  much  lanthanum  w as  left 
in  solution  the  remaining  rare  earth  material  was  precipitated  with 
oxalic  acid  and  the  oxalate  dried  and  weighed.  510  grams  of  dried 
oxalate  were  obtained.  The  oxalate  was  reduced  by  ignition  and  dis- 
solved in  nitric  acid.  The  amount  of  solution  was  thus  decreased 
considerably  and  the  praseodymium  lines  showed  plainly  in  the  abeorp 
tion  spectrum.  Thereupon  magnesium  oxide  was  added  to  neutralize 
the  excess,  acidity  and  then  precipitations  were  made  by  treating 
with  2 grams  of  magnesium  oxide.  After  11  further  precipitations 
the  praseodymium  lines  were  invisible  in  the  filtrate.  Upon  con- 
centrating the  solution,  however,  till  crystallization  set  in  on 
cooling,  the  praseodymium  line  at  483  was  visible.  During  these 
last  11  precipitations  120  grams  of  precipitate  were  obtained. 


• • 


7 


Precipitation  by  NH4OH  in  Presence  of  Ammonium  Salts, 

Investigations  by  Prandtl  and  Rauchenberger7  showed  lanthanum 
hydroxide  to  be  appreciably  more  soluble  in  the  presence  of  ammonium 
salts  than  the  hydroxides  of  praseodymium  or  neodymium.  Experiments 
showed  that  the  presence  of  magnesium  or  zinc  increased  the  differ- 
ence in  solubilities.  Accordingly  lanthanum  and  praseodymium  should 
be  readily  separated  by  precipitation  with  ammonium  hydroxide,  using 
the  double  magnesium  nitrates. 

For  the  experimental  work  with  this  method  500  cc.  of  fraction 
-3  of  a double  magnesium  nitrate  series  was  used.  The  fraction  con- 
tained only  a trace  of  neodymium.  It  was  diluted  to  1000  cc.,  50  cc, 
of  4 times  normal  ammonium  nitrate  added,  and  the  solution  heated  to 
boiling.  Thereupon  an  equal  volume  mixture  of  4 normal  ammonium 
hydroxide  and  4 normal  ammonium  nitrate  v/as  added  drop  by  drop  from 
a dropping  funnel  and  the  solution  stirred,  continually  with  a mechan- 
ical stirrer.  After  running  in  the  precipitating  solution  at  the 
rate  of  about  25  drops  per  minute  for  40  minutes  the  solution  was 
filtered  .and  the  precipitate  dried  and  weighed.  7 grams  of  precipi- 
tate were  obtained  which  possessed  a faint  green  color.  The  pre- 
cipitation v/as  repeated  and  the  amount  of  the  precipitate  increased 
somev/hat.  After  7 precipitations  totalling  88  grams  of  precipitate, 
there  we re  no  praseodymium  lines  visible  in  the  absorption  spectrum. 
Upon  concentrating  the  solution  to  crystallization  a very  faint  ap- 
pearance of  line  -483  resulted.  It  was  weaker  than  the  same  line  in 
the  absorption  spectrum  of  the  final  filtrate  from  the  magnesium 
oxide  separation.  The  solution  v/as  then  diluted,  acid.ified  and 


8 


treated  with  oxalic  acid.  66  grams  of  dried  oxalate,  which  gave 
36  grams  of  residue  after  ignition,  were  obtained. 

Partial  Decomposition  of  the  Nitrates. 

For  the  nitrate  decomposition  some  material  containing  only 
lanthanum  and  praseodymium  was  used.  The  solution  contained  about 
100  grams  of  the  oxides  of  these  metals  and  an  approximate  spectro- 
scopic  estimation  showed  about  10  /°  praseodymium.  The  solution 

was  evaporated  carefully  by  heating  in  a casserole  above  a Bunsen 
flame.  The  heating  was  then  continued  till  brown  fumes  of  N02  were 
given  off.  After  a certain  amount  of  decomposition  had  taken  place 
the  heating  was  stopped,  the  fused  mass  allowed  to  cool  and  then 
treated  with  water.  The  residue  was  thoroly  disintegrated  by  boiling 
after  which  it  was  allowed  to  cool  and  filtered,  and  the  precipitate 
dried  and  weighed.  Thirteen  decompositions  were  made  averaging 
slightly  more  than  3 grams  each  of  precipitate.  After  the  13th  pre- 
cipitate had  been  filtered  off  the  filtrate  still  possessed  a slight 
green  color  and  showed  praseodymium  absorption  lines  thru  1 cm.  of 
solution.  The  precipitates  were  not  fractionally  decomposed  since 
the  main  purpose  of  the  determination  v/as  to  compare  the  speed  of 
separation  with  the  other  methods  used. 

V.  COMPARISON  OF  METHODS. 

Of  the  methods  tried  the  method  that  showed  the  most  promising 
results  for  the  separation  of  lanthanum  and  praseodymium  to  obtain 
pure  lanthanum  the  precipitation  method  of  Prandtl  and  Rauchenberger 


, 


- 


* 


9 

seems  the  most  promising  tho  in  this  investigation  pure  lanthanum 
was  not  obtained  thereby. 

The  magnesium  oxide  precipitate  shows  signs  of  giving  pure  lan- 
thanum after  sufficient  precipitations  but  the  yield  would  evidently 
be  comparatively  small.  From  the  foregoing  results  it  is  evident 
that  for  obtaining  pure  lanthanum  the  method  is  not  very  efficient. 
According  to  Spencer3-0,  Muthman  and  Roelig  effected  the  separation 
of  didymium  and  lanthanum  by  a single  operation.  It  is  doubtful 
whether  they  obtained  pure  lanthanum. 

The  first  precipitate  thrown  down  by  the  magnesium  oxide  separa- 
tion has  a greener  appearance  than,  the  corresponding  precipitate  of 
the  Prandtl  and  Rauchenberger  method.  This  may  be  due,  however,  to 
the  fact  that  it  may  have  a different  chemical  composition.  The 
former  is  probably  a basic  nitrate  while  the  latter  is  a simple 
hydroxide.  One  gram  of  each,  precipitated  from  solutions  of  similar 
praseodymium  content  and  dissolved  in  the  same  amount  of  solution 
gave  absorption  bands  very  nearly  similar  in  intensity.  (This 
weight  was  taken  on  an  accurate  balance). 

The  precipitate  obtained  by  magnesium  oxide  is  more  easily  fil- 
tered than  the  other.  The  latter  while  not  gelatinous  when  thrown 
down  in  the  manner  described  above,  does  clog  the  paper  somewhat  and 
filters  with  more  difficulty.  What  may  be  the  better  plan  in  trying 
to  effect  a rapid  separation  of  lanthanum  and  praseodymium  is  to  use 
magnesium  oxide  to  precipitate  the  greater  part  of  the  praseodymium 
and  then  use  the  other  method  for  removing  the  remainder.  Whether 


10 

the  last  traces  of  praseodymium  can  be  removed  by  it  cannot  be  said 
at  this  writing. 

The  nitrate  decomposition  should  work  well  if  heated  gradually 
in  an  electric  furnace  where  the  heat  would  be  uniform  but  as  worked 
out  in  the  open  casserole,  heated  with  a Bunsen  flame,  evidently  too 
much  local  action  takes  place,  due  to  superheating  at  the  contact  of 
the  residue  with  the  dish.  It  may  work  better  for  smaller  amounts 
even  as  v/orked  out  in  this  investigation  but  for  the  amount  used  it 
fails  to  produce  a very  rapid  separation. 

VI.  SUMMARY. 

1.  Three  methods  for  the  separation  of  lanthanum  and  praseody- 
mium were  tried  out  with  the  following  results: 

(a)  The  partial  decomposition  of  the  nitrates  as  carried 
out  in  an  open  casserole  over  a Bunsen  flame  is  not  satis- 
factory. 

(b)  The  magnesium  oxide  precipitation  effects  a rapid 
separation  up  to  a certain  praseodymium  concentration  after 
which  it  removes  the  praseodymium  only  very  slowly. 

(c)  The  method  of  Prandtl  and  Rauchenberger  consisting 
of  the  precipitation  by  ammonia  in  the  presence  of  ammonia 
salts  apparently  gives  the  best  results  for  obtaining  pure 
lanthanum. 

2.  A comparison  of  these  methods  was- made. 


11 


VII.  BIBLIOGRAPHY. 

1.  Mosander.  Annalen  48  210-23  (1843);  J.  pr.  Gherri .50  276-92 

(1843);  Pogg.  Ann. 60  307-15  (1843);  Phil.  Mag. 23  241-54 
(1843). 

2.  Mendeleeff.  J.  Russ.  Chem.  Ges.j5  119-30  (1873);  Liebig's 

Ann. 168  45-63  (1873);  Ber.6  558  (1873);  St.  Petersb. 
Acad.  Sci.  Bull . 16  45-51  (1871). 

3.  von  Wellsbach.  Monatech.6  477-91  (1885);  Sitzber.  K.  Akad. 

Wiss.  Wien. 92  II.  317-31  (1885). 

4.  Brossbach.  Ber.35.  2826-31  (1902). 

5.  Spencer.  The  Metals  of  the  Rare  Earths,  pp. 31-32  (1919). 

6.  Spencer.  The  Metals  of  the  Rare  Earths,  p.28  (1919). 

7.  Prandtl  and  Rauchenberger . Zeit.  Anorg.  Chem. 120  120-8 

(1922);  Berichte  53  759-69  (1920);  Chem.  Abs.L4  2305 
(1920);  Chem.  Abs.16  1189-90  (1922). 

8.  Hofmann  and  Krftss.  Zeit.  Anorg.  Chem, 5 89-91  (1893). 

9.  Dennis  and  Lemon.  J.  Amer.  Chem.  Soc.-39  151-37  (1915). 

10.  Spencer.  The  Metals  of  the  Rare  Earths,  p.35  (1919). 


m 


